From Japan's damaged nuclear complex: radiation and fear

The dangers are invisible and yet loom large for the disaster-weary population of Japan and beyond.

In the roughly 400 years that most humans have lived with growing technological complexity, the human brain has evolved little. The sights, sounds and smells of the risks we have created ourselves — hulking industrial power plants, towering cityscapes and supersonic jet aircraft — do not set off visceral alarm bells.

Instead of triggering "fight or flight" orders in the brain's most primitive regions, these complex and manmade risks are processed in parts of the brain responsible for higher reasoning.

But that doesn't make those choices rational, Ropeik says. "Perfectly fact-based rationality is an ideal, but it's also a myth," he says.

Every day, we make decisions about risk — whether to drive to work or ride a bike, for instance, or whether to buy organic or conventionally raised produce. We're rarely aware of the mental shortcuts we use in making those decisions, but cognitive psychologists say they're both powerful and predictable.

Paul Slovic, the University of Oregon psychologist who pioneered the study of risk psychology, calls this process "The Feeling of Risk," which is also the title of his 2010 book. It is the gut reaction to a potential source of danger that predisposes us to accept or reject it.

For starters, humans tend to downplay the dangers of the devil they have already learned to live with —burning fossil fuels to generate electricity — and to distort those that are unfamiliar, such as nuclear power.

Our perceptions of personal control over the risks we face make a difference too. Humans tend to feel more comfortable with radiation to which we expose ourselves voluntarily. The same person who would calmly accept her radiation exposure from a series of X-rays or a cross-country flight might fret for days over slightly elevated radiation levels from the Fukushima plant, even though they are much less dangerous, Ropeik says.

Finally, cognitive scientists know that we are far more scared of catastrophic risks that affect a lot of people in one place all at once than we are of risks that take their toll in slow motion, spread broadly across the human landscape. The deaths of 34,000 people in motor vehicle accidents last year does not rivet our attention. But a plane crash that claims the lives of 228 passengers at a time — such as the 2009 disappearance of an Air France jet over the Atlantic Ocean while en route from Rio de Janeiro to Paris — induces horror.

This stems from an impulse that evolutionary psychologists recognize as key to our survival as a species.

"Instinctively, we are more afraid of something that threatens to wipe out our species all at once," Ropeik says.